|An example of two states of human existence, in terms of an initial state (day one) and final state (day 360x) of Gibbs free energy, for a typical pair of reactive single humans (human molecules) in their early 20s. |
In systems where a three-variable equation of state represents the state of the system, such as:
f(P, V, T) = 0
the state of the system is completely determined by any two of the three variables, as long as the variables are independent. Subsequently, for such three-variable defined systems, a single point on a two-dimensional Cartesian coordinate system plot, for any two of these three variables, such as on a pressure-volume indicator diagram, thus defines the state of the system. 
Polish solid state physicist and thermodynamicist Michal Kurzynski argues that the concept of state is embodied in what he calls the "principle of mechanical determinism", as initially formulated by English physicist Isaac Newton at the late 17th century, which can be stated in modern terms as follows:
"The laws of motion and the state of a physical system at a given moment in time unambiguously and uniquely determine the state of the system at all other moments of time, both in the future and in the past."
The term "state" seems to have been first used in a descriptive sense, particularly in the context of thermodynamics, in 1851 by English physicist James Joule who referred to the internal energy of a body as follows: 
“U is the mechanical energy of a body in a given state.”
The more detailed description of the state of a given body was described by American mathematical physicist Willard Gibbs in the 1870s.  In origins, the term stems from the 17th century work on developing the ideal gas laws and the equations of state that resulted.
|Visualization of the concept of "state", by two positions of a pendulum, whereby a body, in an initial state 0, held under the initial constraint of the force X0 of the pendulum arm, is brought to a new state 1 through the application of a displacing force X1, which drives the system (or body) to a new equilibrium state, which is determined by both the contraints X0 and X1.  |
A single point on the PV plane, representative of two of the three variables of a f(P,V,T)=0 state equation, defines the state of the system. 
The following are related quotes:
“Man is the result of a purposeless and materialistic process that did not have him in mind. He was not planned. He is a state of matter, a form of life, a sort of animal, and a species of the order primates, akin nearly or remotely to all of life and indeed to all that is material.”— George Simpson (1967), The Meaning of Evolution 
● Belief state
1. Perrot, Pierre. (1998). A to Z of Thermodynamics, Oxford: Oxford University Press.
2. Joule, James. (1851). Trans. Royal Soc. of Edinburgh, Vol. xx., pg. 475. (as referenced on pg. 31 of Clausius’ 1879 Mechanical Theory of Heat).
3. (a) Gibbs, J. Willard. (1873). "Graphical Methods in the Thermodynamics of Fluids", Transactions of the Connecticut Academy, I. pp. 309-342, April-May.
(b) Gibbs, J. Willard. (1873). "A Method of Geometrical Representation of the Thermodynamic Properties of Substances by Means of Surfaces", Transactions of the Connecticut Academy, II. pp.382-404, Dec.
(c) Gibbs, Willard. (1876). "On the Equilibrium of Heterogeneous Substances", Transactions of the Connecticut Academy, III. pp. 108-248, Oct., 1875-May, 1876, and pp. 343-524, may, 1877-July, 1878.
4. Reiss, Howard. (1965). Methods of Thermodynamics (diagram, pg. 16). Dover.
5. Fermi, Enrico. (1936). Thermodynamics (pg. 2). Prentice-Hall.
6. Thims, Libb. (2010). “Gibbs Free Energy and Human States”, HumanChemistry101, YouTube.com, Dec 21.
7. Kurzynski, Michal. (2006). The Thermodynamic Machinery of Life (pg. 9). New York: Springer.
8. (a) Simpson, George G. (1967). The Meaning of Evolution: a Study of the History of Life and of its Significance for Man (purposeless, 3+ pgs; quote, pg. 345). Harvard University Press.
(b) Strobel, Lee. (2004). The Case for a Creator: a Journalist Investigates Scientific Evidence that Points Toward God (pg. 26). Zondervan, 2009.
● State (physics) – Wikipedia.